STUDY ON THE DEVELOPMENT OF THE EMBRYO AND LARVA OF AMERICAN SHAD,ALOSA SAPIDISSIMA

The American shad(Alosa sapidissima) is a potential aquaculture species with high economic value just like the Chinese shad(Tenualosa reevesii).The fertilizing eggs of American shad were introduced from West coast of American in 2008 and the observation of morphological development of larva and juvenile of American shad were car-ried on.Under the water temperature of 20.3℃-21.9℃,the duration of hatching lasted 82h,according to the morpho-logical characteristics,the embryonic development of Alosa sapidissima may be divided into 7stages: the fertilized egg stage,the cleavage stage,the blastula stage,the gastrula stage,the neural stage,the organogenesis stage and the hatching stage.The fertilizing egg of Alosa sapidissima was spherical,semibuoyant and no oil globule with diameter of 2.85-3.28 mm.The total length of the newly hatched larva was(8.56±0.36) mm and the volume of the yolk sac was(4.57±0.77) mm3 by using the formula of V=4/3π·R/2·(r/2)2.The mouth and anus opened during 1 day after hatching(DAH),meanwhile the brain began to development and the pectoral fin had formed.The volume of the yolk sac of the 2-day-old larva was(0.71±0.23) mm3,just 15.54% of the newly hatched larva.Larva growth and development depend on the energy of yolk sac from newly hatched larva to 3DAH.Then larva entered a mixed feeding stage,finally the larva exhausted all the yolk sac and undertaken exogenous feeding stage in 4DAH,the relationship between the volume of the yolk sac(V) and the hour after hatching(h) was V=4.1583e0.0356h(R2=0.9901).Then the dorsal fin,caudal fin rays,anal fin rays and pelvic fin rays appeared in the late-stage larva and meanwhile the notochord flexion began on 9DAH.Fin ray of each fin completely developed.The scale occurred on 27DAH,the ontogeny of 33DAH juvenile went into the fingerling stages.The regression equation of the relationship between body total length(TL) and age in days(D) was TL=0.0049D2+0.5091D +9.2578(R2=0.9885).